The present invention relates to semiconductor device assembly and, more particularly, to a method of attaching a bond wire to a bond pad of an integrated circuit die.
Many semiconductor devices use bond wires for connecting bond pads of an integrated circuit die to leads of a lead frame or pads of a substrate. As integrated circuits have become smaller and include more functionality, they also include more input and output pads on the surface of the die and thus, the die bond pads have become smaller in size. In addition, there has been a push to switch from gold bond wires to copper bond wires because copper is less expensive and has better electrical characteristics. However, copper also is stiffer so presents difficulties for fine pitch wire bonding.
One issue that arises when attaching a copper wire to a bond pad is known as aluminum splash. For a bond pad that has a layer of conductive metal such as copper that is covered with a cap layer typically of aluminum to prevent the conductive metal from oxidizing, and a layer of passivation that defines a bond pad opening, when the copper wire is bonded to the bond pad using, for example, ultrasonic bonding, the rubbing of the copper wire against the aluminum cap layer heats the aluminum and causes it to splash. If the aluminum splashes outside of the bond pad opening, such as onto to the passivation layer, it can compromise the bond and possibly cause a short circuit with an adjacent bond pad. This aluminum splash issue is exacerbated as the size of the bond pad opening decreases. Thus, it would be advantageous to be able to attach a copper bond wire to a bond pad having an aluminum cap layer and a very small bond pad opening without excessive aluminum splash.